In this video clip, you'll see that the nudibranch swims upwards but, when it wants to go down, it just stops moving and gently drifts back down to the ocean bottom. You'll also see that I am pointing my dive light at the animal and how this makes colours look different underwater.

Juvenile Steller sea lion visitation 2011-02-12.

Divers during safety stop on June 27th in the Blackfish Archipelago, Northern Vancouver Island. Divers are Jacqui Engel and Glen Miller. The abundant plantkon is a testimony to the richness of this cold-water marine ecosystem. Jackie Hildering behind the camera.

White-ringed ribbon worm.
See blog posting on this species at http://themarinedetective.com/2011/01/10/wonder-worm/

The giant nudibranch pounces on its favourite food, the tube-dwelling anemone. The anemone's defence is to retract. Realize the nudibranch is not getting eaten! I did not capture it on video, but the nudibranch withdrew with anemone tentacles in its mouth.